Beam splitting apparatus, transmittance measurement apparatus, and exposure apparatus

ABSTRACT

A beam splitting apparatus generates, from incident light having a specific polarization, first and second split light that has the specific polarization.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to beam splitting systems forsplitting incident light, and measuring systems using the beam splittingsystems. The inventive beam splitting system is suitable for a lightintensity control unit for monitoring a light intensity of anultraviolet (UV) pulse laser, such as an excimer laser as a lightsource.

[0002] The present invention also relates to measuring systems utilizingoptical mechanisms, and more particularly to an apparatus for measuringthe transmittance of a sample using the UV light. The present inventionis suitable, for example, for an apparatus for measuring thetransmittance of an optical element using a UV pulse laser as a lightsource.

[0003] Along with the recent demand on smaller and lower profileelectronic devices, minute semiconductor devices to be mounted ontothese electronic devices have been increasingly demanded. In order tomeet this demand, various proposals have been made to improve exposureresolution. The quality of an image to be transferred onto a wafer, etc.is significantly affected by the illumination performance, e.g.,distributions of illumination on the mask and wafer planes. Therefore,in order to provide high quality semiconductor wafers, LCDs, andthin-film magnetic heads, accurate exposure amount control is necessary.

[0004] An exposure amount control apparatus typically splits light froma light source using a half mirror, etc., receives it via a lightreceiving element, and feedback-controls a light intensity of the lightsource so that a light intensity fluctuation at the illuminated area mayfall within a permissible range. The half mirror is provided, forexample, after an optical integrator, in a position equivalent to apattern on a reticle or mask (these terms are interchangeably used inthis application).

[0005] Use of a shorter wavelength has been promoted to improveresolution. The light source changes from a KrF excimer laser (with awavelength of about 248 nm) to an ArF excimer laser (with a wavelengthof about 193 nm). An F₂ excimer laser (with a wavelength of about 157nm) is about to be put to practical use. An optical element in anoptical system in the exposure apparatus requires the high transmissionproperty for UV light supplied from the light source and high resistanceto the UV light so that it seldom attenuates transmittance for long-timeexposure. The optical element must be fully examined for itstransmission property and UV resistance, and thus its transmittance hasbeen measured frequently.

[0006] A transmittance measurement apparatus typically splits a UV laserbeam of an object excimer laser using a half mirror by reflecting andtransmitting it, receives a reflected beam (a reference beam) by onesensor, receives the transmitted beam (or tested beam) by another sensorafter the transmitted beam transmits through a sample, and measures thesample's transmittance by calculating a ratio between light intensitiesdetected with and without the sample.

[0007] On the other hand, an exposure amount control apparatus typicallysplits light from the light source using a half mirror, receives it viaa sensor, and feeds back the light intensity of the light source so thatfluctuations in the light intensity in the illumination area may fallwithin a permissible range. A half mirror is provided, for example,after an optical integrator, in a position equivalent to a pattern on areticle.

[0008] A conventional exposure amount control apparatus andtransmittance measurement apparatus disadvantageously cannot accuratelydetect the light intensity, resulting in insufficient exposure amountcontrol and transmittance measurement. As well, they cannot provide highquality devices with good exposure performance such as a throughput.

[0009] As a result of eager studies over causes of this problem, theinstant inventors have discovered that the conventional erroneous lightintensity detection results in polarized fluctuation of laser beam. Ahalf mirror has different reflectance and transmittance for p and spolarization components of the laser beam. The polarizations of twobeams split by the half mirror fluctuate when the laser beam (i.e.,light incident on the half mirror) has polarized fluctuation. Thepolarized fluctuation occurs when a polarization component of the laserbeam incident upon a half mirror fluctuates in accordance with theoscillation voltage or changes for each pulse. In case, the sensorcannot accurately detect the light intensity of the laser beam because aratio of light intensities between incident and split light fluctuatesdue to a fluctuated polarizations between the beam incident on the halfmirror and the split light that has passing through the half mirror.

BRIEF SUMMARY OF THE INVENTION

[0010] Accordingly, it is an exemplified object of the present inventionto provide a beam splitting apparatus that enables accurate detectionand control over a light intensity of a light source.

[0011] Another exemplary object of the present invention is to provide atransmittance measurement apparatus and an exposure apparatus, which canaccurately detect the transmittance of a sample.

[0012] A beam splitting apparatus according to one aspect of the presentinvention generates, from incident light having a specific polarization,first and second split light, each of which has the specificpolarization. This beam splitting apparatus can generate the first andsecond split light while making the polarizations of the first andsecond split light the same as that of the incident light.

[0013] A beam splitting apparatus of another aspect of the presentinvention includes a first splitting part for generating, from incidentlight having a specific polarization, first split light that has thespecific polarization, and a second splitting part for generating, fromthe incident light, second split light that has the specificpolarization. This beam splitting apparatus can generate first splitlight at the first splitting part while making the polarization of thefirst split light the same as that of the incident light. This beamsplitting apparatus can generate second split light at the secondsplitting part while making the polarization of the second split lightthe same as that of the incident light.

[0014] A beam splitting apparatus of still another aspect of the presentinvention includes a first splitting part for generating first splitlight so that incident light having a specific polarization is reflectedas a p polarization component for the first time and then reflected asan s polarization component for the second time, and a second splittingpart for generating second split light so that the incident light havinga specific polarization has transmitted as the p polarization componentfor the first time and then transmitted as the s polarization componentfor the second time. This beam splitting apparatus can make the firstsplit light have the same polarization as that of the incident light byreflecting the p polarization component, when the incident light isreflected for the first time at the first splitting part, for the secondtime as the s polarization component. This beam splitting apparatus canmake the second split light have the same polarization as that of theincident light by transmitting the p polarization component, when theincident light has transmitted for the first time at the secondsplitting part, for the second time as the s polarization component.

[0015] A beam splitting apparatus of another aspect of the presentinvention includes a first optical member for reflecting andtransmitting incident light having a specific polarization to generatereflected light and transmitted light, a second optical member that usesthe reflected beam to generate first split light having the specificpolarization, and a third optical member that uses the transmitted lightto generate second split light having the specific polarization. Thissplitting apparatus installs the third optical member to make the lighthaving transmitted through the first optical member have the samepolarization as that of the incident light. Specifically, the secondoptical member reflects the reflected light as a linear polarizedcomponent orthogonal to that reflected by the first optical member. Thethird optical member transmits the transmitted light as a polarizedcomponent orthogonal to that having transmitted through the firstoptical member. Such second and third optical members, which reflect andtransmit the specific linear polarized component of the incident lightas a linear polarized component that is orthogonal to the linearpolarized component, perform an operation to make the split light havethe same polarization as that of the incident light. For example, thefirst to third members may have the same reflectance and transmissionproperties. The first to third members may be plane parallel plates, andthe plane parallel plates are arranged such that their incident angle is45°.

[0016] A light intensity detecting apparatus of another aspect of thepresent invention includes one of the above beam splitting apparatuses,and a detector for detecting a light intensity of either one of thefirst and second light split by the beam splitting apparatus. This lightintensity detecting apparatus includes the above beam splittingapparatus, and exhibits a similar operation. This light intensitydetecting apparatus can use the detector to detect split light that hasthe same polarization as that of the incident light, thus detecting theamount of the split light accurately even when the polarization of theincident light fluctuates.

[0017] A light intensity control unit includes the above light intensitydetecting apparatus, and a control part for controlling a lightintensity of the incident light based on a detection result of thedetector in the light intensity detecting apparatus. This lightintensity control unit includes the above light intensity detectingapparatus, and exhibits a similar operation. This light intensitycontrol unit controls the light intensity of the incident light based ondetection result of the light intensity detecting apparatus, thuscontrolling the incident light accurately.

[0018] A light intensity detecting apparatus of another aspect of thepresent invention includes two of the above beam splitting apparatuses,arranged such that a sample is interposed in between, a first detectorthat detects a light intensity of either one of the first and secondlight split by one of the two beam splitting apparatuses, and a seconddetector that detects a light intensity of either one of the first andsecond light split by the other one of the two beam splittingapparatuses.

[0019] A transmittance measurement apparatus of another aspect of thepresent invention includes the above light intensity detecting apparatusand a processing unit for calculating transmittance of the sample basedon a ratio between detection results by the first and second detectorsin the light intensity detecting apparatus with and without the sample.This transmittance measurement apparatus includes the above lightintensity detecting apparatus, and exhibits a similar operation. It ispossible to accurately measure the transmittance by calculating a ratiobetween detection results at the processing unit with and without thesample.

[0020] A light intensity detecting apparatus of another aspect of thepresent invention includes a plurality of the above beam splittingapparatuses, and a detector for detecting a light intensity of one ofmultiple beams split by the plurality of beam splitting apparatuses.This light intensity detecting apparatus includes a plurality of theabove beam splitting apparatuses, and exhibits a similar operation. Thislight intensity detecting apparatus can use a detector to detectmultiple split beams that have the same polarization as that of theincident beam, and to accurately detect light intensities of multiplesplit beams even when the polarization of the incident light fluctuates.

[0021] A transmittance measurement apparatus of another aspect of thepresent invention includes a first beam splitting part for generatingfirst split beam having a specific polarization from light emitted froma light source, a second beam splitting part for generating, from thefirst split beam, a second split beam having the polarization, a firstdetector for detecting a light intensity of the first split beam, and asecond detector for detecting a light intensity of the second splitbeam, wherein a transmittance of a sample is measured based on adifference between detection results by the first and second detectorswith and without the sample in the first or second split beam. Thistransmittance measurement apparatus can equalize polarizations of thefirst and second split beams. The transmittance measurement apparatusmay further comprise a stage for carrying the sample and removablyinserting the sample onto an optical axis of the first or second splitbeam. This stage can periodically remove the sample from the secondsplit beam (tested beam). Therefore, this transmittance measurementapparatus cancel an offset when a laser beam is not irradiated to thesample by monitoring changes in output ratio. The light source is anultraviolet pulse laser and thus even when a laser beam has polarizedfluctuation in the transmittance measurement apparatus, thepolarizations of the first and second split beams are maintained to beequal. The inventive transmittance measurement apparatus can measure thetransmittance of the sample with accuracy.

[0022] A transmittance measurement apparatus of another aspect of thepresent invention includes a first optical member for reflecting andtransmitting light from a light source to generate reflected andtransmitted beams, a second optical member for transmitting thereflected beam to generate a first split beam having a specificpolarization, a third optical member for reflecting the transmitted beamto generate a second split beam having the specific polarization, afirst detector that detects a light intensity of the first split beam,and a second detector that detects a light intensity of the second splitbeam, wherein a transmittance of a sample is measured based on adifference between detection results by the first and second detectorswith and without the sample in the second split beam. In thistransmittance measurement apparatus, the first and second opticalmembers correspond to the first beam splitting part, and the first andthird optical members correspond to the second beam splitting part, thusexhibiting an operation similar to the above transmittance measurementapparatus.

[0023] The first and second split beams may have an equal number ofreflection times on the first and third optical members and equalpolarization characteristics at the reflections, as well as an equalnumber of transmission times on the first and second optical members andequal polarization characteristics at the transmissions.

[0024] A transmittance measurement apparatus of another aspect of thepresent invention includes a first optical member for reflecting andtransmitting light emitted from a light source to generate reflected andtransmitted beams, and uses the reflected beam as a first split beamhaving a specific polarization, a second optical member for transmittingand reflecting the transmitted beam to generate transmitted andreflected beams, a third optical member for reflecting the transmittedbeam generated by the second optical member to generate a second splitbeam having the specific polarization, a first detector for detecting alight intensity of the first split beam, and a second detector fordetecting a light intensity of the second split beam, wherein atransmittance of a sample is measured based on a difference betweendetection results by the first and second detectors with and without thesample in the second split beam. In this transmittance measurementapparatus, the first optical member corresponds to the first beamsplitting part, and the first to third optical members correspond to thesecond beam splitting part, thus exhibiting an operation similar to theabove transmittance measurement apparatus.

[0025] The first and second split beams may have an equal number ofreflection times on the first and third optical members and equalpolarization characteristics at the reflections, while the secondoptical member transmits the transmitted beam as a linear polarizationcomponent orthogonal to that having transmitted the first opticalmember.

[0026] A transmittance measurement apparatus of another aspect of thepresent invention includes a first optical member for reflecting andtransmitting light emitted from a light source to generate reflected andtransmitted beams, and uses the reflected beam as a first split beamhaving a specific polarization, a second optical member for transmittingand reflecting the transmitted beam to generate transmitted andreflected beams, a third optical member for transmitting the reflectedbeam generated by the second optical member to generate a second splitbeam having the specific polarization, a first detector for detecting alight intensity of the first split beam, and a second detector fordetecting a light intensity of the second split beam, wherein atransmittance of a sample is measured based on a difference betweendetection results by the first and second detectors with and without thesample in the second split beam. In this transmittance measurementapparatus, the first optical member corresponds to the first beamsplitting part, and the first to third optical members correspond to thesecond beam splitting part, thus exhibiting an operation similar to theabove transmittance measurement apparatus.

[0027] The first and second split beams may have an equal number ofreflection times on the first and second optical members and equalpolarization characteristics at the reflections, while the third opticalmember transmits the transmitted beam as a linear polarization componentorthogonal to that having transmitted the first optical member.

[0028] A transmittance measurement apparatus of another aspect of thepresent invention includes a first optical member for reflecting andtransmitting light emitted from a light source to generate reflected andtransmitted beams, and uses the transmitted beam as a first split beamhaving a specific polarization, a second optical member for transmittingand reflecting the transmitted beam to generate transmitted andreflected beams, a third optical member for reflecting the transmittedbeam generated by the second optical member to generate a second splitbeam having the specific polarization, a first detector for detecting alight intensity of the first split beam, and a second detector fordetecting a light intensity of the second split beam, wherein atransmittance of a sample is measured based on a difference betweendetection results by the first and second detectors with and without thesample in the second split beam. In this transmittance measurementapparatus, the first optical member corresponds to the first beamsplitting part, and the first to third optical members correspond to thesecond beam splitting part, thus exhibiting an operation similar to theabove transmittance measurement apparatus.

[0029] The first and second split beams may have an equal number oftransmission times on the first and second optical members and equalpolarization characteristics at the transmissions, while the thirdoptical member reflects the reflected beam as a linear polarizationcomponent that is orthogonal to that having reflected on the firstoptical member.

[0030] A transmittance measurement apparatus of another aspect of thepresent invention includes a first optical member for reflecting andtransmitting light emitted from a light source to generate reflected andtransmitted beams, and uses the transmitted beam as a first split beamhaving a specific polarization, a second optical member for transmittingand reflecting the reflected beam to generate transmitted and reflectedbeams, a third optical member for transmitting the reflected beamgenerated by the second optical member to generate a second split beamhaving the specific polarization, a first detector for detecting a lightintensity of the first split beam, and a second detector for detecting alight intensity of the second split beam, wherein a transmittance of asample is measured based on a difference between detection results bythe first and second detectors with and without the sample in the secondsplit beam. In this transmittance measurement apparatus, the firstoptical member corresponds to the first beam splitting part, and thefirst to third optical members correspond to the second beam splittingpart, thus exhibiting an operation similar to the above transmittancemeasurement apparatus.

[0031] The first and second split beams may have an equal number oftransmission times on the first and second optical members and equalpolarization characteristics at the transmissions, while the thirdoptical member reflects the reflected beam as a linear polarizationcomponent that is orthogonal to that having reflected on the firstoptical member. The first, second, and third members may be opticalelements having the same reflectance and transmittance properties. Thefirst, second, and third members may be plane parallel plates. The planeparallel plates may be arranged such that an incident angle is 45°.

[0032] An optical element fabricated from the sample havingtransmittance of a specific value or higher, measured by the abovetransmittance measurement apparatus. Such an optical element may be alens, a diffraction grating, an optical film, and a combination thereof.The transmittance of such an optical element has been measuredaccurately and the optical element has reliable optical performance.

[0033] An exposure apparatus of another aspect of the present inventionthat uses ultraviolet light, deep ultraviolet light and vacuumultraviolet light as exposure light, irradiates the light onto an objectto be exposed via an optical system including the above optical element.Such an exposure apparatus includes a member having reliable opticalperformance in UV, far UV, and vacuum UV light, thus realizing anaccurate (high-resolution) exposure.

[0034] An exposure apparatus of another aspect of the present inventionincludes an illumination optical system which uses light emitted from alight source to illuminate a mask, on which a desired pattern iscreated, one of the above beam splitting apparatuses, provided in aposition approximately conjugate with the mask, a detector for detectinga light intensity of either one of the first and second light split bythe beam splitting apparatus, and a control part for controlling a lightintensity of the light source based on a detection result by thedetector. Such an exposure apparatus includes the above beam splittingapparatus, and exhibits a similar operation. This detector canaccurately detect an exposure amount without influence by a fluctuatingpolarization characteristic of the illumination optical system. Thus,such an exposure apparatus can control the exposure amount accurately,thus realizing an exposure with accuracy. A device fabricating methodand a device as a product using such an exposure apparatus also functionas an aspect of the present invention.

[0035] Other objects and further features of the present invention willbecome readily apparent from the following description of theembodiments with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a schematic perspective view showing a light intensitydetecting apparatus that includes a splitting means as one aspect of thepresent invention.

[0037]FIG. 2A is a side view showing a first plane parallel plate shownin FIG. 1 on a plane ZY. FIG. 2B is a side view showing a second planeparallel plate shown in FIG. 1 on a plane XY. FIG. 2C is a side viewshowing a third plane parallel plate shown in FIG. 1 on a plane ZX.

[0038]FIG. 3 is a schematic perspective view showing a variation of thelight intensity detecting apparatus shown in FIG. 1.

[0039]FIG. 4 is a schematic perspective view showing another variationof the light intensity detecting apparatus shown in FIG. 1.

[0040]FIG. 5 is a schematic perspective view showing still anothervariation of the light intensity detecting apparatus shown in FIG. 1.

[0041]FIG. 6 is a schematic side view showing part of an exposureapparatus that includes a beam splitting part as one aspect of thepresent invention.

[0042]FIG. 7 is a view showing a measurement result of a transmittancebaseline before a polarization is considered.

[0043]FIG. 8 is a view showing a measurement result of a transmittancebaseline using the light intensity detecting apparatus shown in FIG. 3.

[0044]FIG. 9 is a block diagram showing a transmittance measurementapparatus of one aspect of the present invention.

[0045]FIG. 10 is a schematic perspective view showing part of thetransmittance measurement apparatus shown in FIG. 1.

[0046]FIG. 11A is a side view showing a first plane parallel plate shownin FIG. 10 on a plane ZX. FIG. 11B is a side view showing a second planeparallel plate shown in FIG. 10 on a plane ZX. FIG. 11C is a side viewshowing a third plane parallel plate shown in FIG. 10 on a plane ZX.

[0047]FIG. 12 is a view corresponding to FIG. 10, showing part of atransmittance measurement apparatus that includes a variation of thebeam splitting part shown in FIG. 9.

[0048]FIG. 13A is a side view showing a first plane parallel plate shownin FIG. 12 on a plane ZX. FIG. 13B is a side view showing a second planeparallel plate shown in FIG. 12 on a plane ZY. FIG. 13C is a side viewshowing a third plane parallel plate shown in FIG. 12 on a plane ZX.

[0049]FIG. 14 is a view corresponding to FIG. 10, showing part of atransmittance measurement apparatus including a variation of the beamsplitting part shown in FIG. 12.

[0050]FIG. 15A is a side view showing the first plane parallel plateshown in FIG. 14 on a plane ZX. FIG. 15B is a side view showing a secondplane parallel plate shown in FIG. 14 on a plane XY. FIG. 15C is a sideview showing the third plane parallel plate shown in FIG. 14 on a planeZX.

[0051]FIG. 16 is a view corresponding to FIG. 10, showing part of atransmittance measurement apparatus that includes a variation of thebeam splitting part shown in FIG. 9.

[0052]FIG. 17A is a side view showing a first plane parallel plate shownin FIG. 16 on a plane ZX. FIG. 17B is a side view showing a second planeparallel plate shown in FIG. 16 on a plane ZX. FIG. 17C is a side viewshowing a third plane parallel plate shown in FIG. 16 on a plane XY.

[0053]FIG. 18 is a view corresponding to FIG. 10, showing part of atransmittance measurement apparatus including a variation of the beamsplitting part shown in FIG. 16.

[0054]FIG. 19A is a side view showing the first plane parallel plateshown in FIG. 18 on a plane ZX. FIG. 19B is a side view showing thesecond plane parallel plate shown in FIG. 18 on a plane ZY. FIG. 19C isa side view showing the third plane parallel plate shown in FIG. 18 on aplane XY.

[0055]FIG. 20 is a flowchart for explaining a fabrication of devices(such as semiconductor chips like ICs and LSIs, LCDs, CCDs, and thelike).

[0056]FIG. 21 is a flowchart for a wafer process of step 4 shown in FIG.20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Referring to accompanying drawings, a description will now begiven of a light intensity detecting apparatus 100 including a beamsplitting part 10 as one aspect of the present invention and an exposureapparatus 200 including the beam splitting part 10. In each figure, thesame reference numeral indicates the same element. The same referencenumeral having an alphabetic capital letter is a variation of thathaving no alphabetic letter, and a reference numeral with no alphabeticletter generalizes reference numerals with alphabetic letters unlessotherwise specified. FIG. 1 is a schematic perspective view showing alight intensity detecting apparatus 100 that includes the beam splittingpart 10. FIG. 6 is a schematic side view showing part of the exposureapparatus 200 that includes the beam splitting part 10.

[0058] A description will now be given of the light intensity detectingapparatus 100 that includes the beam splitting part 10. As shown in FIG.1, the light intensity detecting apparatus 100 is a measurement systemfor detecting a light intensity from a light source L, and includes thebeam splitting part 10 and a detector 110. The light detecting apparatus100 provides the beam splitting part 10 on the optical axis of light L1emitted from the light source L, and the detector 110 in place to detectat least one of beams L2 and L3 split by the beam splitting part 10.FIG. 1 assumes that a traveling direction of the light L1 is a Z-axis, adirection vertical to the Z-axis in a plane of the light source L is anX-axis, and a normal direction to the plane of the light source L is aY-axis. Although the detector 110 is provided on the side of the lightL2 in FIG. 1, this structure is for exemplary purposes only and thus itmay detect the beam L3. As described later, when the light intensitydetecting apparatus 100 serves to measure the transmittance, the lightsource L may be one element in the light intensity detecting apparatus100.

[0059] The beam splitting part 10 generates two split beams L2 and L3from the light L1 from the light source L so that these beams have thesame polarization of that of the light L1. The beam splitting part 10includes three plane parallel plates (i.e., first, second and thirdplane parallel plates 20-40). The first plane parallel plate 20 isarranged on the optical axis of the light L1 from the light source L.The second plane parallel plate 30 is arranged, with a specificlimitation, on the optical axis of light reflected by the first planeparallel plate 20. The third plane parallel plate 40 is arranged on theoptical axis of light that has transmitted through the first planeparallel plate 20, with the specific limitation as described later. Theplane parallel plates 20-40 can be an optical element such as a beamsplitter and the like, but is not limited to this as long as theyexhibit an operation required by the present invention. In order tomaintain high efficiency to the split beams and to deliver the beams todetectors with minimized loss, beam splitters themselves are alsorequired to have high durability and high transmittance at thewavelength of the light source. When using high energy light sources,such as KrF, ArF and F₂ excimer lasers with short wavelengths, thethickness of the beam splitters, whether they are cubes or parallelplates, must be minimized. Especially with pulsed lasers, theinstantaneous energy can be very high and may give damages to thematerials of beam splitters. For use with UV, DUV, VUV and high energypulsed light sources, plane parallel plates are often preferred as thebeam splitters. Similarly, the plane parallel plates 20-40 preferably,but are not limited to, have the same reflection and transmissionproperties as long as they meet the relationship below.

[0060] The first plane parallel plate 20 reflects and transmits thelight L1, thereby splitting it into two beams. As shown in FIGS. 1 and2A, the first plane parallel plate 20 is arranged such that the incidentplane of the light L1 is in parallel to the X-axis, and its normaldirection of the incident plane forms 45° with the optical axis of thelight L1. Here, FIG. 2A is a side view showing the first plane parallelplate 20 on the plane ZY. FIG. 2B is a side view showing the secondplane parallel plate 30 on a plane XY. FIG. 2C is a side view showingthe third plane parallel plate 40 on a plane ZX. It is noted that thefirst plane parallel plate 20 does not necessarily have the above setangle as long as it may split the light L1 into two.

[0061] From the light reflected by the first plane parallel plate 20,the second plane parallel plate 30 generates the light L2 that has thesame polarization as that of the light L1. As shown in FIG. 1, the lightL1 from the light source L may be split basically using the first planeparallel plate 20 to reflect and transmit the light L1. Nevertheless,the beam splitting part 10 arranges the second plane parallel plate 30relative to the first plane parallel plate 20, to generate the beam L2having the same polarization as that of the light L1.

[0062] As shown in FIGS. 1 and 2B, when the first plane parallel plate20 is arranged to form 45° with the Z-axis, the second plane parallelplate 30 is arranged such that the incident plane of the light reflectedon the first plane parallel plate 20 is in parallel to the Z-axis, andits normal direction of the incident plane forms 45° with the opticalaxis of this reflected light. Of course, the present invention is notlimited only to such a value. Rather, the second plane parallel plate 30may be arranged such that the beam L2 has the same polarization as thatof the light L1. Part of the light, reflected by the first planeparallel plate 20, transmits the second plane parallel plate 30 and thenis absorbed by a damper (not shown). This may prevent transmittingcomponent of the beam L2 from becoming flare.

[0063] From the light that has transmitted through the first planeparallel plate 20, the third plane parallel plate 40 generates the lightL3 that has the same polarization as that of the light L1. As discussed,the light L1 from the light source L may be split basically using theplane parallel plate 20 to reflect and transmit the light L1.Nevertheless, the inventive beam splitting part 10 arranges the thirdplane parallel plate 40 relative to the plane parallel plate 20, togenerate the beam L3 that has the same polarization as that of the lightL1.

[0064] As shown in FIGS. 1 and 2C, when the first plane parallel plate20 is arranged to form 45° with the Z-axis, the third plane parallelplate 40 is arranged such that the incident plane of the light havingtransmitted through the first plane parallel plate 20 is in parallel tothe Y-axis, and the normal direction of the incident plane forms 45°with the optical axis of this transmitted light. Of course, the presentinvention is not limited to such a value, and the third plane parallelplate 40 may be arranged such that the beam L3 has the same polarizationas that of the light L1. In this structure, the third plane parallelplate 40 further transmits the light that has transmitted through theplane parallel plate 20, generating the beam L3 having the samepolarization as that of the light L1. The third plane parallel plate 40reflects the light, but a damper (not shown) absorbs this reflectedlight. This may prevent a reflected component of the light L3 frombecoming flare.

[0065] The detector 110 detects the light intensity of the incidentlight. The detector 110 is arranged on the optical axis of the beams L2and/or L3. The detector includes a light receiving element andprocessor, measuring the light intensity of the light. Any knowntechnique is applicable to the detector, and a detailed descriptionthereof will be omitted. Light detected by the detector 110 will bediscussed in detail in the description of the operation given later.

[0066] A description will now be given of the operation of the inventivelight intensity detecting apparatus 100. The light L1 is initiallyemitted from the light source L. It is, for example, a UV pulse lasersuch as an excimer laser. The first plane parallel plate 20 reflects andtransmits the light L1 from the light source L, splitting it into twobeams. Where I_(H) and I_(V) are intensities of horizontal and verticalcomponents of the light L1 in FIG. 1, the polarization of the light L1may be expressed by the following equation 1. $\begin{matrix}\frac{{I_{H} - I_{V}}}{I_{H} + I_{V}} & (1)\end{matrix}$

[0067] The reflected light and transmitted light are further reflectedand transmitted by the second and third plane parallel plates 30 and 40.The light reflected by the second plane parallel plate 30 becomes thelight L2, and a damper shields the transmitted light. The light that hastransmitted through the third plane parallel plate 40 becomes the beamL3, and a damper shields the reflected light. As discussed, the secondand third plane parallel plates 30 and 40 are arranged such that thelight L2 and L3 have the same polarization as that of light L1.

[0068] The intensities of the horizontal and vertical components of thelight L2 can be expressed by equations 2 and 3: $\begin{matrix}{r_{s}^{2}r_{p}^{2}I_{V}} & (2) \\{r_{p}^{2}r_{s}^{2}I_{H}} & (3)\end{matrix}$

[0069] where r is a Fresnel reflection coefficient, and subscripts p ands are polarization components at the time of reflection. Using theseequations 2 and 3, the polarization of the light L2 may be expressed bythe equation 4: $\begin{matrix}{\frac{{{r_{s}^{2}r_{p}^{2}I_{V}} - {r_{p}^{2}r_{s}^{2}I_{H}}}}{{r_{s}^{2}r_{p}^{2}I_{V}} + {r_{p}^{2}r_{s}^{2}I_{H}}} = \frac{{I_{H} - I_{V}}}{I_{H} + I_{V}}} & (4)\end{matrix}$

[0070] Notably, the equation 4 shows that the light L2 reflected by thefirst and second plane parallel plates 20 and 30 has the samepolarization as that of the light L1.

[0071] The intensities of the horizontal and vertical components of thelight L3 may be expressed by equations 5 and 6: $\begin{matrix}{t_{pr}^{2}t_{p}^{2}t_{sr}^{2}t_{s}^{2}I_{H}} & (5) \\{t_{sr}^{2}t_{s}^{2}t_{pr}^{2}t_{p}^{2}I_{V}} & (6)\end{matrix}$

[0072] where t is a Fresnel transmission coefficient, subscripts p and sare polarization components at the time of transmission, and a subscriptr is a side of an exit plane of the plane parallel plate. From theseequations 5 and 6, the polarization of the light L3 may be expressed bythe equation 7: $\begin{matrix}{\frac{{t_{pr}^{2}t_{p}^{2}t_{sr}^{2}t_{s}^{2}I_{H}} - {t_{sr}^{2}t_{s}^{2}t_{pr}^{2}t_{p}^{2}I_{V}}}{{t_{pr}^{2}t_{p}^{2}t_{sr}^{2}t_{s}^{2}I_{H}} + {t_{sr}^{2}t_{s}^{2}t_{pr}^{2}t_{p}^{2}I_{V}}} = \frac{{I_{H} - I_{V}}}{I_{H} + I_{V}}} & (7)\end{matrix}$

[0073] Understandably, the equation 7 shows that the light L3, which isreflected by the first and third plane parallel plates 20 and 40, hasthe same polarization as that of the light L1.

[0074] The inventive light intensity detecting apparatus 100 uses thebeam splitting part 10 having three plane parallel plates 20-40, andprovides split beams (i.e., L2 and L3) with the same polarization asthat of the light L1. As discussed, this structure requires the secondand third plane parallel plates 30 and 40 to be arranged such that thebeams L2 and L3 have the same polarization as that of the light L1. Thismeans that the second and third plane parallel plates 30 and 40 need tobe arranged such that the polarizations of the beams L2 and L3 reflectedand transmitted by these plates meets the equation 1.

[0075] A description will now be given of the way of detection of thelight intensity of the light source L by the detector 110 arranged onthe optical path of the light L2 and/or L3. In the light intensitydetecting apparatus 100 of the present embodiment, each of the splitbeams L2 and L3 has the same polarization as that of the incident lightL1. Even when the light L1 fluctuates, the light intensity detectingapparatus 100 can detect the light intensities of the beams L2 and L3accurately because a ratio between light intensities of the light L2 andL3 relative to the light L1 does not change.

[0076] While the detector 110 is arranged on the optical axis of thebeam L2, a sample may be arranged on the optical path of the beam L3 andthe detector may be arranged on the optical path of the beam that hastransmitted through the sample. The light intensity measuring apparatus100 serves as a transmittance measurement apparatus using this structureto measure a ratio between light intensities with and without thesample. This structure uses as a tested beam the beam L3 havingtransmitted twice through the plane parallel plates 20 and 40. Thereby,the light intensity of the light source L may be detected with accuracy,when a high power light intensity is supplied onto the sample, withoutinfluence by polarized fluctuation of the light source L. This structureuses as a detection beam the beam L2 that was reflected twice on theplane parallel plate, and thus it serves as a light-attenuating meanssuch as an ND filter to adjust the intensity of a UV pulse laser beamfor desired energy density. This may reduce measurement errors caused bythe components of the ND filter and others, and monitor the lightintensity of the light L1 with accuracy.

[0077] In the above structure of the transmittance measurement, when thesample is arranged on the optical path of the light L2 (between thesecond plane parallel plate 30 and the detector 110), it is possible tomonitor the light intensity of a laser beam when the low power lightintensity is supplied to the sample, since the light L2 havingtransmitted a plane parallel plate twice is used as a tested beam.

[0078] In the above light intensity detecting apparatus 100, a controlpart may be provided for controlling the light intensity of the lightsource L based on a detection result by the detector 110. As a result,the light intensity detecting apparatus also serves as a light intensitycontrol unit.

[0079] Referring to FIG. 3, a description will now be given of a lightintensity detecting apparatus 100A as a variation of the light intensitydetecting apparatus 100. Here, FIG. 3 is a schematic perspective viewshowing the light intensity detecting apparatus 100A as a variation ofthe light intensity detecting apparatus 100. The light intensitydetecting apparatus 100A combines two splitting means 10 shown in FIG. 1so as to serve as a light intensity detecting apparatus for measuringthe transmittance of a UV pulse laser beam, etc. As shown in FIG. 3, thelight intensity detecting apparatus 100A further includes a splittingmeans 10 (shown as a splitting means 10 a in FIG. 3) for splitting thebeam L3 of the light intensity detecting apparatus 100 shown in FIG. 1.Since the light intensity detecting apparatus 100A uses the similarcomponents to those of the light intensity detecting apparatus 100, adetailed description thereof will be omitted.

[0080] As in the above light intensity detecting apparatus 100, thelight L1 from the light source L is split into two beams L2 and L3 bythe splitting means 10. The detector 110 for detecting the lightintensity of the light L2 is provided on the optical path of the beamL2, and the sample is arranged on the optical path of the light L3. Thelight L3 having transmitted the sample is split into two beams L4 and L5by the splitting means 10 a on the optical path of the light L3. Thedetectors 120 and 130 are arranged on the optical paths of the beams L4and L5, respectively.

[0081] In this structure, from signal beams of the reference beam (L2)and the tested beam (L4) detected by the detectors 110 and 120,intensity ratio is calculated as (tested beam voltage average/referencebeam voltage average). From the intensity ratio I measured with thesample in the tested beam and the intensity ratio 10 measured withoutthe sample, the sample's transmittance for the UV pulse laser beam iscalculated as T=I/10. The detector 130 connected to the beam L5 is usedto detect the power of the laser beam from the light source L.

[0082] This light intensity detecting apparatus 101A uses the beam L2 asa tested beam, which has transmitted the plane parallel plate twice. Thelight intensity of the laser beam may be detected when a high powerlight intensity is irradiated to the sample. For the above reasons, allof the beams (L2, L4, and L5) detected by three detectors (not shown)have the same polarization as that of the light L1 from the light sourceL. Thus, it is possible to detect the light intensity of the laser beamaccurately without influence by polarized fluctuation of the laser beamfrom the light source L. A transmittance of an optical member, etc., maybe measured for the UV pulse laser beam.

[0083] The light intensity detecting apparatus 100A uses as a signalbeam the beam having transmitted a plane parallel plate twice. Thus,such a plane parallel plate also serves as a light-attenuating meanssuch as an ND filter to adjust the intensity of a UV pulse laser beamfor desired energy density. This may accurately reduce measurementerrors caused by the components of the ND filter and the like. Theamount of the laser beam may be monitored with accuracy. Thetransmittance of the optical member, etc., may be also measuredaccurately for the UV pulse laser beam.

[0084] Referring to FIGS. 7 and 8, it is understood in view of theconventional structure, the light intensity detecting apparatus 100Amaintains high detection accuracy. Here, FIG. 7 is a view showing ameasurement result of a transmittance baseline before a countermeasureis taken for the polarization. FIG. 8 is a view showing a measurementresult of the transmittance baseline using the light intensity detectingapparatus shown in FIG. 3. The horizontal axis in the figure is thenumber of laser pulses [Mpls], and the vertical axis is a transmittancebaseline [%].

[0085]FIG. 7 shows that the deviation of the baseline is 0.32% when nocountermeasure is taken for the polarization. In the light intensitydetecting apparatus 10A, on the other hand, the deviation of thebaseline is 0.09%. Since the measurement accuracy is below 0.1% when thepolarization is preserved using the beam splitting part 10, themeasurement accuracy is three times as high as that in FIG. 7. Thisresult assures the usefulness of the inventive beam splitting part 10.

[0086] Referring FIG. 4, a description will be given of a lightintensity detecting apparatus 100B as another variation of the lightintensity detection apparatus 100. Here, FIG. 4 is a schematicperspective view showing a light intensity detecting apparatus 100B asanother variation of the light intensity detection apparatus 100. Thelight intensity detecting apparatus 100B combines two splitting means 10shown in FIG. 1 so as to serve as a light intensity detecting apparatusfor measuring the transmittance of a UV pulse laser beam, etc. As shownin FIG. 4, the light intensity detecting apparatus 100B further includesa splitting means 10 (shown as a splitting means 10 b in FIG. 4) forsplitting the light L2 of the light intensity detecting apparatus 100.Since the light intensity detecting apparatus 100B uses the similarcomponents to those of the light intensity detecting apparatus 100, adetailed description thereof will be omitted.

[0087] As in the above light intensity detecting apparatus 100, thelight L1 from the light source L is split into two beams L2 and L3 bythe beam splitting part 10. The light intensity detecting apparatus 100Barranges a detector 140 on the optical path of the beam L3, and a sampleon the optical path of the beam L2. The beam having transmitted thesample is split by the splitting means 10 b arranged on the optical pathof the beam L3 into two beams L6 and L7. Detectors 150 and 160 arearranged on the optical paths of the beams L6 and L7, respectively.

[0088] In this structure, the light intensity detecting apparatus 100Bcalculates an intensity ratio as (tested beam voltage average/referencebeam voltage average) from signal beam of the reference and tested beamsdetected by the detectors 140 and 150. Thus, the intensity ratio Imeasured with the sample in the tested beam (beam L2) and the intensityratio I0 measured without the sample, the sample's transmittance for theUV pulse laser beam is calculated as T=I/I0. The detector 160 connectedto the beam L7 is used to detect the power of the laser beam.

[0089] This light intensity detecting apparatus 100B uses as a testedbeam the beam L2, which has transmitted the plane parallel plate twice.The light intensity of the laser beam may be detected when a low powerlight intensity is supplied to the sample. The light detected by thedetectors connected to the beams L3, L6, and L7 have the samepolarization as that of the light L1 from the light source L. As aresult, the light intensity of the laser beam may be monitoredaccurately without influence by polarized fluctuation of the laser beamL1 from the light source L. The transmittance of the optical member,etc., may also be measured accurately for the UV pulse laser beam.

[0090] As discussed, by combining two splitting means 10, the lightintensity detecting apparatuses 100A and 10B can monitor the lightintensity of the laser beam when high and low power light intensitiesare supplied to the sample. The light intensity of the laser beam may bemonitored with accuracy without influence by polarized fluctuation ofthe laser beam. The transmittance of the optical member, etc., may alsobe monitored accurately for the UV pulse laser beam.

[0091] Referring to FIG. 5, a description will be given of a lightintensity detecting apparatus 100C as still another variation of thelight intensity detecting apparatus 100. Here, FIG. 5 is a schematicperspective view showing the light intensity detecting apparatus 100C asstill another variation of the light intensity detecting apparatus 100.The light intensity detecting apparatus 100C combines three or moresplitting means 10 shown in FIG. 1 so as to serve as a light intensitydetecting apparatus for evaluating linearity and the like of aphoto-sensor, etc. As shown in FIG. 5, the light intensity detectingapparatus 100C includes splitting means 10 in series (shown exemplarilyas two splitting means 10 c and 10 d in FIG. 5) for splitting the lightL3 of the light intensity detecting apparatus 100 shown in FIG. 1. Sincethe light intensity detecting apparatus 100C uses the similar componentsto those of the light intensity detecting apparatus 100, a detaileddescription thereof will be omitted.

[0092] In this structure, the light L1 from the light source L cangenerate as many beams as the number of splitting means 10 like thebeams L2, L4, L8, . . . , by connecting the splitting means 10 shown inFIG. 1 in parallel. Detectors (not shown) are arranged, for example, onthe optical path of the beams L2, L4, L8, . . . , and light intensitiesof beams detected by these detectors are monitored. In this lightintensity detecting apparatus 100C, like the above light intensitydetecting apparatus 100, each laser beam detected by the detector hasthe same polarization as that of the light L1 from the light source L.The light intensity of a laser beam may be monitored with accuracywithout influence by polarized fluctuation of the laser beam of thelight source L. It is also possible to accurately evaluate linearity andthe like of a photo-sensor, etc., for the UV pulse laser beam.

[0093] The light intensity detecting apparatus 100C detects as a signalbeam the beam reflected twice on a plane parallel plate. This planeparallel plate serves as a light-attenuating means such as an ND filter,etc. to adjust the intensity of the UV pulse laser beam for desiredenergy density. This may reduce causes of measurement errors due tocomponents, and monitor the light intensity of a laser beam withaccuracy. It is also possible to accurately measure linearity and thelike of a photo-sensor, etc., for the UV pulse laser beam.

[0094] Referring to FIG. 6, a description will be given of an exposureapparatus 200 that includes the beam splitting part 10 as one aspect ofthe present invention. As shown in FIG. 6, the exposure apparatus 200includes an illumination apparatus including an illumination opticalsystem, a mask (not shown), a projection optical system (not shown), anda control part (not shown). The exposure apparatus 200 is a projectionexposure apparatus that exposes a pattern created on the mask onto awafer W in a step-and-scan manner. The “step-and-scan” manner, as usedherein, is one mode of exposure method which exposes a mask pattern ontoa wafer by continuously scanning the wafer relative to the mask, and bymoving, after a shot of exposure, the wafer stepwise to the nextexposure area to be shot.

[0095] The illumination apparatus 210 typically includes laser 220 as alight source and an illumination optical system, thus illuminating themask (not shown) on which a pattern to be transferred is created.

[0096] The laser 220 is a light source that emits illumination light,e.g., an F₂ excimer laser with a wavelength of about 157 nm. However,the laser 220 may be replaced with an ArF excimer laser with awavelength of about 193 nm, etc.

[0097] The illumination optical system is an optical system thatirradiates a beam to the mask (not shown), and includes an opticalsystem 230, an optical integrator (or a light integrator) 240, acondensing lens 250, a beam splitting part 260, a blade (stop) 270, andan imaging lens (not shown). An optical element fabricated from thesample having a transmittance of a preset value or higher, and measuredby the transmittance measurement apparatus of the present invention, isapplicable to optical elements such as lenses for the illuminationoptical system.

[0098] The optical system 230 includes a plurality of lenses, and forms,for example, an afocal system that is telecentric at incidence and exitsides. The afocal system (optical system 230) in this system enables tocontinuously magnify and demagnify light (at the beam cross-section of acoherent beam) from the laser 220 into two directions orthogonal at theoptical axis.

[0099] The optical integrator, which is, for example, a fly-eye lens,uniformly illuminates the mask (not shown) efficiently.

[0100] The condensing lens 250 is, for example, a condenser lens, andcondenses as many beams from the optical integrator 240 as possible,superimposes them onto the stop 270, and Koehler-illuminates the blade270 via the beam splitting part 260.

[0101] The beam splitting part 260 has three plane parallel plates asshown in FIG. 1, and splits condensed light into transmitted light andreflected light. The splitting method preserves the polarization of abeam as discussed above. In the present embodiment, the transmittedlight split by the beam splitting part 260 illuminates the stop 270. Thereflected light split by the beam splitting part 260 enters the detector262 for detecting the light intensity.

[0102] The imaging lens (not shown) forms an image on the mask from thelight having passed through the stop 270. Any technique known in the artis applicable to the illumination optical system 210 in the exposureapparatus 200, and thus a detailed description will be omitted.

[0103] A desired pattern is created on the mask, and diffracted lightfrom the mask passes through a projection optical system (not shown),and forms a pattern image onto the wafer. The wafer is an object to beexposed such as a wafer and a liquid crystal plate, onto which resist isapplied.

[0104] The projection optical system (not shown) may use an opticalsystem solely composed of a plurality of lens elements, an opticalsystem comprised of a plurality of lens elements and at least oneconcave mirror, and an optical system comprised of a plurality of lenselements and at least one diffractive optical element such as akinoform. An optical element fabricated from the sample with atransmittance of a preset value or higher, and measured by the inventivetransmittance measurement apparatus is applicable to optical elementssuch as lenses for the projection optical system.

[0105] The control part (not shown) typically includes CPU, and amemory, which is connected to the detector 260. Regardless of its name,the CPU may covers an MPU or any other processor for controlling theoperation of each section. The memory includes a ROM and RAM, and storesfirmware operating the exposure apparatus, and data on an optimalexposure amount (or illuminance). In this embodiment, the control partfeeds back the light intensity of the laser 220 so that the fluctuationof the light intensity detected by the detector 262 may fall within apermissible range.

[0106] The thus-structured exposure apparatus 200 exhibits the followingoperations: The exposure apparatus 200 uses the illumination apparatus210 to illuminate the mask, and exposes a desired mask pattern onto thewafer via the projection optical apparatus (not shown). Simultaneously,the control part (not shown) of the exposure apparatus 200 feeds backthe light intensity of the laser 220 based on the light intensitydetected by the detector 262, i.e., the illuminance to illuminate themask, so that the fluctuation of the light intensity may fall within apredetermined range.

[0107] As discussed, in the inventive beam splitting part 260, the lightentering the splitting means and the split light have the samepolarization. Therefore, the exposure apparatus 200 can accuratelycontrol the exposure light intensity regardless of a change inpolarization characteristic in the illumination optical systems due tothe polarized fluctuation of the laser 220. An optical elementfabricated from a sample with the transmittance of a preset value orhigher and measured by the transmittance measurement apparatus of thepresent invention is applicable to optical elements such as lenses foruse with the illumination optical system so as to realize accurate (highresolution) exposure using an optical element that has reliable opticalperformance in the UV light, far UV light and vacuum UV light. Thethroughput will improve due to illumination with uniform light intensityand provide a precise pattern transfer to the resist, thus providinghigh-quality devices (such as semiconductor devices, LCD devices,photographing devices (such as CCDs, etc.), thin film magnetic heads,and the like).

[0108] A description will now be given of a transmittance measurementapparatus 300 including a beam splitting part 320 as one aspect of thepresent invention. FIG. 9 is a block diagram of a transmittancemeasurement apparatus 300.

[0109] Referring to FIGS. 9-11, a description will be given of thetransmittance measurement apparatus 300 as one aspect of the presentinvention. Here, FIG. 10 is a schematic perspective view of part of thetransmittance measurement apparatus 300. FIG. 10 assumes that atraveling direction of the beam L1 emitted from a light source 310 is aZ-axis, a direction vertical to the Z-axis in a plane of the lightsource 310 is an X-axis, and a normal direction to the plane of thelight source 310 is a Y-axis. FIG. 11 is a view for explaining the beamsplitting part 320. FIG. 11A is a side view showing a first planeparallel plate 322 on a plane ZX. FIG. 11B is a side view showing asecond plane parallel plate 324 on a plane ZX. FIG. 11C is a side viewshowing a third plane parallel plate 326 on a plane ZX. Thetransmittance measurement apparatus 300 is a measuring apparatus thatuses the light from the light source 310 to measure the transmittance ofa sample S, and includes the light source 310, the beam splitting part320, detectors 340 and 350, a stage 360, and a control part 370.

[0110] As shown in FIG. 9, the beam splitting part 320, detectors 340and 350, and stage 360 are housed in a measurement chamber 302 thatdefines a different atmosphere from the outside (although themeasurement chamber 302 is not shown in FIG. 10). The light source 310,detectors 340 and 350, and stage 360 are electrically connected to thecontrol part 370 located outside of the measurement chamber 302. Thelight source 310 is arranged such that a (tested) beam can be radiatedto the sample on the stage 360 in the measurement chamber 302. Themeasurement chamber 302 not only defines the measurement space, but alsocreates an atmosphere different than outside of the measurement chamber302 using, for example, nitrogen gas, so as to measure the transmittanceof the sample S with accuracy. Nitrogen gas prevents a laser beam fromgenerating ozone, and keeps oxygen from absorbing the laser beam, thuscontributing to the improvement of accuracy in measuring the sample'stransmittance. Of course, the gas that forms the atmosphere of themeasurement chamber 302 is not limited to the nitrogen gas, and otherinert gases are applicable. Using stainless steel, aluminum, etc. tobuild the measurement chamber 302 would prevent the measurement chamberfrom becoming a source of contamination for the measurement space.

[0111] The light source 310 emits a specific beam to the sample S, andis made up of, for example, a UV pulse laser, such as an excimer laser,etc. The transmittance measurement apparatus 300 of this embodiment maybe suitable for measurement of the transmittance of the sample S usingan UV pulse laser for the light source 310, but other kinds of lightsources (e.g., a xenon lamp, and others) may be applied for the lightsource 310. The transmittance measurement apparatus 300 of thisembodiment does not preclude transmittance measurement for the sample Sin this structure.

[0112] The beam splitting part 320 splits the beam L1 from the lightsource 310 into a reference beam L2 and a tested beam L3 as well asintroducing the reference beam L2 and tested beam L3 to the detectors340 and 350. The beam splitting part 320 of this embodiment also servesto make a correction so that the reference beam L2 and the tested beamL3 entering the detectors 340 and 350 may have the same polarization.

[0113] As shown in FIG. 10, the beam splitting part 320 exemplarilyincludes three plane parallel plates (i.e., first, second and thirdplane parallel plate 322, 324, and 326), and the second and third planeparallel plates 324 and 326 are provided on the beam split by the firstplane parallel plate 322 with a specific limitation described later. Ofcourse, the arrangement of the three parallel plates is not limited tothe configuration shown in FIG. 10 as far as the beams incident upon thedetectors 340 and 350 are arranged such that their polarizations areequal.

[0114] Preferably, the three plane parallel plates (322 to 326) are madeup of plane parallel plates having the same reflectance andtransmittance, but they may be configured by optical elements such asbeam splitters, and the like. In order to maintain high efficiency tothe split beams and to deliver the beams to detectors with minimizedloss, beam splitters themselves are also required to have highdurability and high transmittance at the wavelength of the light source.When using high energy light sources, such as KrF, ArF and F2 excimerlasers with short wavelengths, the thickness of the beam splitters,whether they are cubes or parallel plates, must be minimized. Especiallywith pulsed lasers, the instantaneous energy can be very high and maygive damages to the materials of beam splitters. For use with UV, DUV,VUV and high energy pulsed light sources, plane parallel plates areoften preferred as the beam splitters. When using plane parallel plates,the polarization states of the back surface reflected beams aretheoretically equal to those of corresponding beams and thus will notcause errors in the measurement of transmittance. With the longcoherency of the light source 310, surface reflection beams and backreflection beams of the three plane parallel plates (322 to 326) mayinterfere with each other. The plane parallel plates 322 to 326 may havea slight wedge angle to avoid the interference. In case, the wedge angleshould be so much as to generate several interference fringes caused bya beam overlap or as no beam overlap seen at the light receiving plane(not shown) of the detectors 340 and 350.

[0115] The first plane parallel plate 322 reflects and transmits thebeam L1 emitted from the light source 310 to generate the reflected beamand the transmitted beam, thus splitting the beam L1 emitted from thelight source 310. As shown in FIGS. 10 and 11A, the first plane parallelplate 322 is arranged such that its incident plane upon the beam L1 isparallel to the Y-axis and a normal direction of the incident planeforms 45° with the optical axis of such a beam. Understandably, thefirst plane parallel plate 322 is not limited to such a setting angle asfar as it is so arranged that a beam emitted from the light source 310is split into two.

[0116] The second plane parallel plate 324, which corrects the reflectedbeam split by the first plane parallel plate 322, generates the beam(reference beam) L2 having the same reflection and transmissionproperties (i.e., the same polarization) as the beam (tested beam) L3entering the detector 350, as well as introducing the reference beam L2to the detector 340. Specifically, the second plane plate 324 generatesthe beam L2 while transmitting the beam reflected by the first planeparallel plate 322 so that its transmission property may be the same asthat of the beam L3.

[0117] As shown in FIGS. 10 and 11B, when the first plane parallel plate322 is arranged to form 45° with the Z-axis, the second plane parallelplate 324 is arranged such that the incident plane of the reflected beamreflected by the first plane parallel plate 322 is parallel to theY-axis and the normal direction of the incident plane forms 450 with theoptical axis of such a reflected beam. The present invention is notlimited only to this value as far as the second plane parallel plate 324is arranged such that the beam L2 has the same reflection andtransmission properties. Part of the beam reflected by the first planeparallel plate 322 will be reflected by the second plane parallel plate324, but such a reflected beam will be absorbed by a damper 306 providedin the measurement chamber 302. This will prevent a reflection componentof the beam L2 from becoming flare.

[0118] The third plane plate 326, which corrects the transmitted beamsplit by the first plane parallel plate 322, generates the beam (testedbeam) L3 having the same reflection and transmission properties (i.e.,the same polarization) as the beam (reference beam) L2 entering thedetector 340, as well as introducing the tested beam L3 to the detector350. Specifically, the third plane plate 326 serves to generate the beamL3 while reflecting the beam transmitted by the first plane parallelplate 322 so that its reflection property may be the same as that of thebeam L2.

[0119] As shown in FIGS. 10 and 11C, when the first plane parallel plate322 is arranged such that it forms 45° with the Z-axis, the third planeparallel plate 326 is arranged such that the incident plane of thetransmitted beam transmitted by the first plane parallel plate 322 isparallel to the Y-axis and the normal direction of the incident planeforms 45° with the optical axis of such a reflected beam. The presentinvention is not limited only to this value as far as the third planeparallel plate 324 is arranged such that the beam L3 has the samereflection and transmission properties as the beam L2. The third planeparallel plate 326 transmits part of the incident beam, but such atransmitted beam will be absorbed by a damper 304. This will prevent atransmitted component of the beam L3 from becoming flare.

[0120] With reference to FIGS. 12 and 13, the beam splitting part 320may be replaced with a beam splitting part 320 a. Here, FIG. 12 is aview corresponding to FIG. 10, showing a transmittance measurementapparatus 300 a that includes a beam splitting part 320 a, which is avariation of the beam splitting part 320 shown in FIG. 9. FIG. 13 is aview for explaining the beam splitting part 320 a shown in FIG. 12. FIG.13A is a side view showing a first plane parallel plate 322 on a ZXplane. FIG. 13B is a side view showing a second plane parallel plate 328on a plane ZY. FIG. 13C is a side view showing a third plane parallelplate 326 on a plane ZX. Similar to the beam splitting part 320, thebeam splitting part 320 a splits the beam L1 from the light source 310into the reference beam L2 and the tested beam L3, as well asintroducing these reference beam L2 and tested beam L3 to the detectors340 and 350. The beam splitting part 320 a serves to make a correctionso that the reference beam L2 and the tested beam L3 entering thedetectors 340 and 350 respectively have the same polarization.

[0121] As shown in FIG. 12, the beam splitting part 320 a exemplarilyincludes three plane parallel plates (a first plane parallel plate 322,a second plane parallel plate 328, and a third plane parallel plate326), and the second and third plane parallel plates 328 and 326 areprovided on the beam transmitted by the first plane parallel plate 322with a specific limitation described later. The beam splitting part 320a is different from the beam splitting part 320 in that the beamsplitting part 320 arranges the second plane parallel plate 324 in thebeam reflected by the first plane parallel plate 322, while the beamsplitting part 320 a arranges the second plane parallel plate 328 in thebeam transmitted by the first plane parallel plate 322. The rest of thestructure is the same.

[0122] The second plane parallel plate 328, which corrects thetransmitted beam split by the first plane parallel plate 322,contributes to the generation of the beam (tested beam) L3 having thesame polarization as the beam (reference beam) L2 entering the detector340. Specifically, the second plane parallel plate 328 transmits alinear polarization component, having transmitted the first planeparallel plate 322, as a linear polarization component that isorthogonal to this linear polarization component, thus contributing tothe generation of the beam L3.

[0123] The second plane parallel plate 328, despite of such a structure,will thus have an effect similar to the second plane parallel plate 324described above.

[0124] As shown in FIGS. 12 and 13B, when the first plane parallel plate322 is arranged to form 45° with the Z-axis, the second plane parallelplate 328 is arranged such that the incident plane of the transmittedbeam transmitted by the first plane parallel plate 322 is parallel tothe X-axis and the normal direction of the incident plane forms 45° withthe optical axis of this transmitted beam. Of course, the presentinvention is not limited only to this value as far as the second planeparallel plate 328 is arranged such that the beam L3 has the samepolarization as that of the beam L3. Part of the beam transmitted by thefirst plane parallel plate 322 will be reflected by the second planeparallel plate 328, but such a reflected beam will be absorbed by adamper 306 a provided in the measurement chamber 302. This will preventa reflection component of the beam L2 from becoming flare.

[0125] The third plane plate 326, which corrects the beam transmitted bythe second plane parallel plate 328, generates the beam (tested beam) L3having the same polarization as the beam (reference beam) L2 enteringthe detector 340, as well as introducing the tested beam L3 to thedetector 350. Specifically, the third plane plate 326 serves to generatethe beam L3 while reflecting the beam reflected by the first planeparallel plate 322 so that the reflected polarization characteristic ofthe incident beam may be the same as that of the beam reflected by thefirst plane parallel plate 322. The way of arranging the third planeparallel plate 326 is the same as that of the above beam splitting part320, and thus a description will be omitted.

[0126] In the beam splitting part 320 a shown in FIG. 12, the secondplane parallel plate 328 is arranged on the optical axis of the beamtransmitted by the first plane parallel plate 322 and before the thirdplane parallel plate 326. However, the structure may be as shown inFIGS. 14 and 15, if the beam L3's polarization is the same as that ofthe beam L2. Here, FIG. 14 is a view corresponding to FIG. 10, showing atransmittance measurement apparatus 300 b including a beam splittingpart 320 b that is of another shape of the beam splitting part 320 ashown in FIG. 12. FIG. 15 is a view for explaining the beam splittingpart 320 b shown in FIG. 14. FIG. 15A is a side view showing the firstplane parallel plate 322 on a ZX plane. FIG. 15B is a side view showinga second plane parallel plate 328 on a plane XY. FIG. 15C is a side viewshowing the third plane parallel plate 326 on a plane ZX.

[0127] As shown in FIG. 14, the second plane plate 328 is provided onthe optical axis of a reflected beam of the third plane parallel plate326. As shown in FIGS. 14 and 15B, when the first plane parallel plate322 is arranged to form 45° with the Z-axis, the second plane parallelplate 328 is arranged such that the incident plane of the reflected beamreflected by the third plane parallel plate 326 is parallel to theZ-axis and the normal direction of the incident plane forms 45° with thebeam of such a reflected beam. Understandably, this structure willexhibit an operation similar to that of the above second plane parallelplate 328.

[0128] Referring to FIGS. 16 and 17, the beam splitting part 320 may bereplaced by a beam splitting part 320 c. Here, FIG. 16 is a viewcorresponding to FIG. 10, showing a transmittance measurement apparatus300 c that includes a beam splitting part 320 c as a variation of thebeam splitting part 320 shown in FIG. 9. FIG. 17 is a view forexplaining the beam splitting part 320 c shown in FIG. 16. FIG. 17A is aside view showing a first plane parallel plate 322 on a ZX plane. FIG.17B is a side view showing a second plane parallel plate 330 on a planeZX. FIG. 17C is a side view showing a third plane parallel plate 326 ona plane XY. Similar to the beam splitting part 320, the beam splittingpart 320 c splits the beam L1 emitted from the light source 310 into thereference beam L2 and the tested beam L3, as well as introducing thesereference beam L2 and tested beam L3 to the detectors 340 and 350.Similar to the beam splitting part 320, the beam splitting part 320 balso serves to make a correction so that the reference beam L2 and thetested beam L3 entering the detectors 340 and 350 respectively may havethe same polarization.

[0129] As shown in FIG. 12, the beam splitting part 320 c exemplarilyincludes three plane parallel plates (the first plane parallel plate322, the second plane parallel plate 330, and the third plane parallelplate 332), and the second and third plane parallel plates 330 and 332are provided on the beam reflected by the first plane parallel plate 322with a specific limitation described later. The beam splitting part 320c is different from the beam splitting part 320 in that the beamsplitting part 320 uses the beam transmitted by the first plane parallelplate 322 as the tested beam, while the beam splitting part 320 c usesthe beam reflected by the first plane parallel plate 322 as the testedbeam.

[0130] The third plane parallel plate 332, which corrects the beam(reflected beam) split by the first plane parallel plate 322,contributes to the generation of the beam (tested beam) L3 having thesame polarization as that of the beam (reference beam) L2 entering thedetector 340. Specifically, the third plane parallel plate 332, whichreflects the linear polarization component, reflected on the first planeparallel plate 322, as a linear polarization component that isorthogonal to this linear polarization component, contributes to thegeneration of the beam L3.

[0131] As shown in FIGS. 16 and 17B, when the first plane parallel plate322 is arranged to form 45° with the Z-axis, the second plane parallelplate 330 is arranged such that the incident plane of the reflected beamreflected by the first plane parallel plate 322 is parallel to theY-axis and the normal direction of the incident plane forms 45° with theoptical axis of this reflected beam. Of course, the present invention isnot limited only to this value as far as the second plane parallel plate330 is arranged such that the beam L3 has the same polarization as thatof the beam L2. Part of the beam will be reflected by the second planeparallel plate 330, but such a reflected beam will be absorbed by adamper 305 provided in the measurement chamber 302. This will preventsuch a reflected beam from becoming flare.

[0132] The second plane plate 330, which corrects the beam (referencebeam) split by the first plane parallel plate 322, generates the beam(tested beam) L2 having the same polarization as the beam (referencebeam) L2 entering the detector 340, as well as introducing the testedbeam L3 to the detector 350. Specifically, the second plane plate 330serves to generate the beam L3 while transmitting the beam reflected bythe first plane parallel plate 322 so that the transmitted polarizationcharacteristic of the incident beam may be the same as that of the beamtransmitted by the first plane parallel plate 322.

[0133] As shown in FIGS. 16 and 17C, when the first plane parallel plateis arranged to form 45° with the Z-axis, the third plane parallel plate332 is arranged such that the incident plane of the reflected beamreflected by the first plane parallel plate 322 is parallel to theZ-axis and the normal direction of the incident plane forms 45° with theoptical axis of this reflected beam. Of course, the present invention isnot limited only to this value as far as the third plane parallel plate332 is arranged such that the beam L3 has the same polarization as thebeam L2. The third plane parallel plate 332 transmits a part of theincident beam, but such a transmitted beam will be absorbed by a damper307. This will prevent a transmitted component of the beam L3 frombecoming flare.

[0134] In the beam splitting part 320 c shown in FIG. 16, the secondplane parallel plate 330 is arranged on the optical axis of the beamtransmitted by the first plane parallel plate 322 and before the thirdplane parallel plate 332. However, the structure may be as shown inFIGS. 18 and 19, if the beam L3's polarization is the same as that ofthe beam L2. Here, FIG. 18 is a view, corresponding to FIG. 10, showinga transmittance measurement apparatus 300 d including a beam splittingpart 320 d as a variation of the beam splitting part 320 c shown in FIG.16. FIG. 19 is a view for explaining the beam splitting part 320 d shownin FIG. 18. FIG. 19A is a side view showing the first plane parallelplate 322 on a plane ZX. FIG. 19B is a side view showing the secondplane parallel plate 330 on a plane ZY. FIG. 19C is a side view showingthe third plane parallel plate 330 on a plane XY.

[0135] As shown in FIG. 18, the second plane plate 330 is provided onthe optical axis of the reflected beam of the third plane parallel plate332. As shown in FIGS. 18 and 19B, when the first plane parallel plate322 is arranged to form 45° with the Z-axis, the second plane parallelplate 330 is arranged such that the incident plane of the reflected beamreflected by the third plane parallel plate 332 is parallel to theX-axis and the normal direction of the incident plane forms 45° with thebeam of this reflected beam. Understandably, this structure will exhibitan operation similar to that of the above second plane parallel plate330.

[0136] The detectors 340 and 350 detect the light mounts of the beams(reference beam L2 and tested beam L3) entering the pertinent detectors,and communicate these light intensities to the control part 370electrically. The detector 340 is arranged on the optical axis of thebeam L2, and the detector 350 on the optical axis of the beam L3, beingelectrically connected to the control part described later. Thedetectors 340 and 350 typically include a light receiving element andprocessor. They may apply any technique known in the art, and a detaileddescription thereof will be omitted.

[0137] The stage 360 carries the sample S, and serves as a mechanism forremovably inserting the sample S onto the transmitting beam. Forexample, referring to FIG. 10, the stage 360 is arranged such that thesample S is positioned on the transmitted beam split by the first planeparallel plate 322. However, the location of the stage 360 is notlimited to this as far as the sample S is positioned on the beamsranging from the first plane parallel plate 322 to the detector 350. Anytechnique known in the art is applicable to the mechanism that removablyinserts the sample S onto the stage 360, and a detailed descriptionthereof will be omitted. The stage 360 may be structured, for example,to move up and down (or right and left) relative to the optical axis sothat such a movement enables the sample on the axis to be inserted andremoved. The stage 360 is electrically connected to the control part370, so that the removable insertion may be realized by the controlpart.

[0138] The control part 370 has CPU and a memory, and controls theoperation of each part of the transmittance measurement apparatus 300.In the present embodiment, based on detection results from the detectors340 and 350, the control part 370 measures the transmittance of thesample S, while it controls the light source 310 and the stage 360. Thecontrol part 370 sends a result of a transmittance measurement to anoutput device not shown (or to an external device including thetransmittance measurement apparatus 300).

[0139] A description will now be given of an operation of thetransmittance measurement apparatus 300 of the present invention. First,from the light source 310, the beam L1 is emitted. Here, the lightsource 310 is, e.g., an UV pulse laser of excimer laser and the like.The beam L1 from the light source 310 is reflected and transmitted bythe first plane parallel plate 322, being split into two beams.

[0140] Referring to FIG. 10, the reflected beam split by the first planeparallel plate 322 as a reference beam transmits the second planeparallel plate 324 arranged on the optical path of the reflected beam,and is received by the detector 340. On the other hand, the transmittedbeam split by the first plane parallel plate 322 as a tested beamtransmits the sample S fixed on the stage 360. The transmitted beam isreflected on the third plane parallel plate 326 arranged on its opticalpath, thus being received by the detector 350. In the above structure,the beams L2 and L3 received by the detectors 340 and 350 are reflectedand transmitted equal times on the plane parallel plates arranged on theoptical path. The polarization characteristics are maintained equal whenthe beams L2 and L3 are reflected and transmitted each time on the planeparallel plate.

[0141] From the signal beams of the reference beam L2 and the testedbeam L3 detected by the detectors 340 and 350, an intensity ratio R(=tested beam voltage mean value/ reference beam voltage mean value) iscalculated. Assuming intensities of a horizontal component and avertical component are I_(H) and I_(V), the light intensity of the lightsource 310 can be expressed as I_(H)+I_(V). The light intensity of thereference beam L2 detected by the detector 340 is expressed by thefollowing equation. $\begin{matrix}{{r_{pr}^{2}t_{p}^{2}r_{p}^{2}I_{H}} + {t_{sr}^{2}t_{s}^{2}r_{s}^{2}I_{V}}} & (8)\end{matrix}$

[0142] The light intensity of the tested beam L3 detected by thedetector 350 is expressed by the following equation. $\begin{matrix}{{r_{p}^{2}t_{pr}^{2}t_{p}^{2}I_{H}} + {r_{s}^{2}t_{sr}^{2}t_{s}^{2}I_{V}}} & (9)\end{matrix}$

[0143] where r and t are a Fresnel reflection coefficient andtransmission coefficient, subscripts p and s are a polarizationcomponent at the time of reflection and transmission, and a subscript ris a side of exit of each plane parallel plate.

[0144] Thus, based on an intensity I determined while the sample S isset up in the beam, and an intensity I_(o) while the sample S is removedfrom the beam, the transmittance T of the sample S for an ultravioletpulse laser beam is calculated as T=I/I_(o). This transmittance is sentto the output device, and thus, a user will know the transmittance ofthe sample S.

[0145] Using the inventive transmittance measurement apparatus 300, theratio R between the light intensity detected by the detector 340 and thelight intensity detected by the detector 350 is constant (R=1)regardless of a change in the light intensity I_(H)+I_(V) of the lightsource 310. Consequently, without influence by the fluctuation of thelight source 310, the ratio between the light intensity of the referencebeam L2 and the light intensity of the tested beams L3 may be measuredwith accuracy. Because R=1, for sensors and the like used as thedetectors 340 and 350, light intensity detection can be conducted withthe same light intensity range for the same kinds of sensors. The S/Nratio of the light intensity detection is high, providing accuratemeasurement.

[0146] In order to eliminate fluctuating transmittance of a planeparallel plate used for this apparatus 300 and causes of measurementerrors due to laser absorption, and the like, by an atmosphere insidethe measuring instrument, the stage may use a removably insertingmechanism that periodically inserts the sample S onto the beam. In otherwords, it is possible to cancel an offset when a laser beam is notirradiated to the sample S by monitoring changes in output ratios fromthe detectors 340 and 350 while periodically the sample is taken out ofthe beam.

[0147] Referring to FIG. 12, the beam L1 from the light source 310 issplit by the first plane parallel plate 322 into two beams, i.e.,transmitted and reflected beams. The reflected beam split by the firstplane parallel plate 322 as a reference beam is received by the detector340, while the transmitted beam split is received by the first parallelplate 322 as a tested beam transmits the sample S fixed to the stage360. This transmitted beam transmits the second plane parallel plate 328arranged on the optical path, further reflects on the third planeparallel plate 326, and is received by the detector 350. In thestructure shown in FIG. 12, the beams L2 and L3 received by thedetectors 340 and 350 have equal reflected polarization characteristicson the first plane parallel plate 322 and the third plane parallel plate326, and the transmitted polarization characteristic of the first planeparallel plate 322 and the transmitted polarization characteristic ofthe second plane parallel plate 322 are orthogonal to each other. Thebeams L2 and L3 has the same polarization.

[0148] In the structure shown in FIG. 12, the light intensity of thebeam L2 detected by the detector 340 can be expressed by the followingequation. $\begin{matrix}{{r_{p}^{2}I_{H}} + {r_{s}^{2}I_{V}}} & (10)\end{matrix}$

[0149] The light intensity of the beam L3 detected by the detector 350is expressed by the following equation. $\begin{matrix}{{t_{pr}^{2}t_{p}^{2}t_{sr}^{2}t_{s}^{2}r_{p}^{2}I_{H}} + {t_{sr}^{2}t_{s}^{2}t_{pr}^{2}t_{p}^{2}r_{s}^{2}I_{V}}} & (11)\end{matrix}$

[0150] Therefore, the ratio R of the light intensities detected by thedetectors 340 and 350 is given in the following fixed equationregardless of a change in light intensity (I_(H)+I_(V)) of the lightsource 310. $\begin{matrix}{R = {t_{pr}^{2}t_{p}^{2}t_{sr}^{2}t_{s}^{2}}} & (12)\end{matrix}$

[0151] Thus, it is possible to accurately measure the ratio of the lightintensity of the reference beam L2 and the light intensity of the testedbeam L3 without influence by the polarized fluctuation of the lightsource 310. The transmittance measurement apparatus 300 a (or thetransmittance measurement apparatus 300 b) can accurately measure atransmittance of an optical member, and the like. By using thetransmitted beam split by the first plane parallel plate 322 as a testedbeam in the transmittance measurement apparatus 300 a (or thetransmittance measurement apparatus 300 b), it is possible to measure atransmittance of a sample S when a high-power light intensity is appliedto it.

[0152] Referring to FIG. 16, the beam L1 from the light source 310 issplit by the first plane parallel plate 322 into two beams, i.e.,transmitted and reflected beams. The transmitted beam split by the firstplane parallel plate 322 as a reference beam is received by the detector340, while the reflected beam split by the first parallel plate 322 as atested beam transmits the sample S fixed to the stage 360. Thistransmitted beam transmits the second plane parallel plate 330 arrangedon the optical path, reflects on the third plane parallel plate 332, andis received by the detector 350. Simultaneously, the beams L2 and L3received by the detectors 340 and 350 have equal transmittedpolarization characteristics on the first plane parallel plate 322 andthe second plane parallel plate, and the reflected polarizationcharacteristic of the first plane parallel plate 322 and the reflectedpolarization characteristic of the third plane parallel plate areorthogonal to each other. Thus, the beams L2 and L3 have the samepolarization.

[0153] In the structure shown in FIG. 18, the light intensity of thebeam L2 detected by the detector 340 can be expressed by the followingequation. $\begin{matrix}{{t_{pr}^{2}t_{p}^{2}I_{H}} + {t_{sr}^{2}t_{s}^{2}I_{V}}} & (13)\end{matrix}$

[0154] The light intensity of the beam L3 detected by the detector 350can be expressed by the following equation. $\begin{matrix}{{t_{pr}^{2}t_{p}^{2}r_{s}^{2}r_{p}^{2}I_{H}} + {t_{sr}^{2}t_{s}^{2}r_{p}^{2}r_{s}^{2}I_{V}}} & (14)\end{matrix}$

[0155] Therefore, the ratio R of the light intensity detected by thelight intensity detecting mechanism and the light intensity detected bythe light intensity detecting mechanism is given in the followingequation. $\begin{matrix}{R = {r_{p}^{2}r_{s}^{2}}} & (15)\end{matrix}$

[0156] The ratio of the light intensities of the reference beam and thetested beam can be measured with accuracy without influence by thepolarized fluctuation of the light source 310. As a result, thetransmittance measurement apparatus 300 c (or the transmittancemeasurement apparatus 300 d) can measure a transmittance of an opticalmember, and the like accurately. By using the transmitted beam split bythe first plane parallel plate 322 as a tested beam in the transmittancemeasurement apparatus 300 c (or the transmittance measurement apparatus300 d), it is possible to measure a transmittance of a sample S when alow-power light intensity is applied to it.

[0157] The transmittance measurement apparatuses 300-300 d in FIGS. 9-19are also applicable to the exposure apparatus 200 shown in FIG. 6. Forexample, an optical element fabricated from the sample having atransmittance of a preset value or higher, and measured by the inventivetransmittance measurement apparatus is applicable to optical elementssuch as lenses for the illumination and projection optical systems.

[0158] Referring to FIGS. 20 and 21, a description will now be given ofan embodiment of a device fabricating method using the above mentionedexposure apparatus 200. FIG. 20 is a flowchart for explaining how tofabricate devices (i.e., semiconductor chips such as IC and LSI, LCDs,CCDs). Here, a description will be given of the fabrication of asemiconductor chip as an example. Step 1 (circuit design) designs asemiconductor device circuit. Step 2 (mask fabrication) forms a maskhaving a designed circuit pattern. Step 3 (wafer making) manufactures awafer using materials such as silicon. Step 4 (wafer process), which isalso referred to as a pretreatment, forms actual circuitry on the waferthrough photolithography of the present invention using the mask andwafer. Step 5 (assembly), which is also referred to as a post-treatment,forms into a semiconductor chip the wafer formed in step 4 and includesan assembly step (e.g., dicing, bonding), a packaging step (chipsealing), and the like. Step 6 (inspection) performs various tests forthe semiconductor device made in Step 5, such as a validity test and adurability test. Through these steps, a semiconductor device is finishedand shipped (Step 7).

[0159]FIG. 21 is a detailed flowchart of the wafer process in Step 4.Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition and the like. Step 14(ion implantation) implants ion into the wafer. Step 15 (resist process)applies a photosensitive material onto the wafer. Step 16 (exposure)uses the exposure apparatus 200 to expose a circuit pattern on the maskonto the wafer. Step 17 (development) develops the exposed wafer. Step18 (etching) etches parts other than a developed resist image. Step 19(resist stripping) removes disused resist after etching. These steps arerepeated, and multi-layer circuit patterns are formed on the wafer. Itis possible to fabricate more high-quality devices than ever by usingthe fabricating method of this embodiment. In this way, the devicefabricating method using this exposure apparatus 200, and devices as asample object are part of the present invention.

[0160] Further, the present invention is not limited to these preferredembodiments, and various variations and modifications may be madewithout departing from the spirit and scope of the present invention.

[0161] According to the beam splitting apparatus of the presentinvention, the light intensity of a UV pulse laser beam from an excimerlaser, etc. as a light source can be split into light having the samepolarization as the incident light without influence by the polarizedfluctuation of the laser beam. A light intensity detecting apparatusincluding such a beam splitting apparatus can use the split light todetect the light intensity with accuracy. When this light intensitydetecting apparatus is used to measure the transmittance, it mayaccurately detect the light intensity of the laser beam andtransmittance of the optical element, thus providing a high-qualityoptical element. The light intensity detecting apparatus including aplurality of inventive beam splitting apparatuses can monitor lightwhose polarization is always equal to that of the incident light, thusaccurately evaluating a photo-sensor's linearity for a light source(laser, etc.).

[0162] Use of the exposure apparatus including this beam splittingapparatus enables detection of an accurate exposure amount regardless ofchanges in polarization characteristics of illumination optical systems,thus performing accurate feedback control of the exposure amount.Therefore, use of such an exposure apparatus not only improvesthroughput, but also serves to provide high-quality devices.

What is claimed is:
 1. A beam splitting apparatus generating, fromincident light having a specific polarization, first and second splitlight, each of which has said specific polarization.
 2. A beam splittingapparatus comprising: a first splitting part for generating, fromincident light having a specific polarization, first split light thathas said specific polarization; and a second splitting part forgenerating, from the incident light, second split light that has saidspecific polarization.
 3. A beam splitting apparatus comprising: a firstsplitting part for generating first split light incident light having aspecific polarization is reflected so that a p polarization componentreflected for the first time is then reflected as an s polarizationcomponent for the second time; and a second splitting part forgenerating second split light so that the incident light having aspecific polarization is transmitted so that a p polarization componenttransmitted for the first time is then transmitted as a s polarizationcomponent for the second time.
 4. A beam splitting apparatus comprising:a first optical member for reflecting and transmitting incident lighthaving a specific polarization to generate reflected light andtransmitted light; a second optical member that uses said reflected beamto generate first split light having the specific polarization; and athird optical member that uses said transmitted beam to generate secondsplit light having the specific polarization.
 5. A beam splittingapparatus according to claim 4, wherein said second optical memberreflects a linear polarization component orthogonal to that reflected bysaid first optical member.
 6. A beam splitting apparatus according toclaim 4, wherein said third optical member transmits said transmittedbeam as a linear polarized component orthogonal to that transmittedthrough said first optical member.
 7. A beam splitting apparatusaccording to claim 4, wherein said first to third optical members havethe same reflection and transmission properties.
 8. A beam splittingapparatus according to claim 4, wherein said first to third members areplane parallel plates.
 9. A beam splitting apparatus according to claim8, wherein the plane parallel plates are arranged such that theirincident angle is 45°.
 10. A light intensity detecting apparatuscomprising: a beam splitting apparatus for generating, from incidentlight having a specific polarization, first and a second split lightthat has said specific polarization; and a detector for detecting alight intensity of either one of the first and second light split bysaid beam splitting apparatus.
 11. A light intensity control unitcomprising: a light intensity detecting apparatus comprising a beamsplitting apparatus for generating, from incident light having aspecific polarization, first and second split light that has saidspecific polarization, and a detector for detecting a light intensity ofeither one of the first and second light split by the beam splittingapparatus; and a control part for controlling a light intensity of theincident light based on a detection result of the detector in said lightintensity detecting apparatus.
 12. A light intensity detecting apparatuscomprising: two beam splitting apparatuses, arranged such that a sampleto be measured is interposed in between, each of which generates, fromincident light having a specific polarization, first and second splitlight that has said specific polarization; a first detector that detectsa light intensity of either one of the first and second light split byone of said two beam splitting apparatuses; and a second detector thatdetects a light intensity of either one of the first and second lightsplit by the other one of said two beam splitting apparatuses.
 13. Atransmittance measurement apparatus comprising: a light intensitydetecting apparatus comprising two beam splitting apparatuses, arrangedsuch that a sample to be measured is interposed in between, each ofwhich generates, from incident light having a specific polarization,first and second split light that has said specific polarization, afirst detector that detects a light intensity of either one of the firstand second light split by one of said two beam splitting apparatuses,and a second detector that detects a light intensity of either one ofthe first and second light split by the other one of said two beamsplitting apparatuses; and a processing unit for calculatingtransmittance of the sample based on a ratio between detection resultsby the first and second detectors in said light intensity detectingapparatus with and without the sample.
 14. A light intensity detectingapparatus comprising: a plurality of beam splitting apparatuses,arranged in serial or parallel, for generating, from incident lighthaving a specific polarization, first and second split light that hassaid specific polarization; and at least one detector for detecting alight intensity of at least one of multiple beams split by saidplurality of beam splitting apparatuses.
 15. An optical elementfabricated from the sample having transmittance of a specific value orhigher, measured by a transmittance measurement apparatus comprising alight intensity detecting apparatus comprising two beam splittingapparatuses, arranged such that a sample to be measured is interposed inbetween, each of which generates, from incident light having a specificpolarization, first and second split light that has said specificpolarization, a first detector that detects a light intensity of eitherone of the first and second light split by one of said two beamsplitting apparatuses, and a second detector that detects a lightintensity of either one of the first and second light split by the otherone of said two beam splitting apparatuses, and a processing unit forcalculating transmittance of the sample based on a ratio betweendetection results by the first and second detectors in said lightintensity detecting apparatus with and without the sample.
 16. Anoptical element according to claim 15, wherein said optical element isone of a lens, a diffraction grating, an optical film, and a combinationthereof.
 17. An exposure apparatus that uses one of ultraviolet light,deep ultraviolet light and vacuum ultraviolet light as exposure light,irradiates the light onto an object to be exposed via an optical systemincluding an optical element according to claim
 16. 18. An exposureapparatus comprising: an illumination optical system which uses lightemitted from a light source to illuminate a mask, on which a desiredpattern is created; a beam splitting apparatus, provided in a positionapproximately conjugate with the mask, for generating, from incidentlight having a specific polarization, first and second split light thathas said specific polarization; a detector for detecting a lightintensity of either one of the first and second light split by said beamsplitting apparatus; and a control part for controlling a lightintensity of the light source based on a detection result by saiddetector.
 19. A device fabricating method comprising the steps of:projecting a pattern on a mask onto an object to be exposed by using anexposure apparatus comprising an illumination optical system which useslight emitted from a light source to illuminate a mask, on which adesired pattern is created, a beam splitting apparatus, provided in aposition approximately conjugate with the mask, for generating, fromincident light having a specific polarization, first and second splitlight that has said specific polarization, a detector for detecting alight intensity of either one of the first and second light split bysaid beam splitting apparatus, and a control part for controlling alight intensity of the light source based on a detection result by saiddetector; and performing a specified operation for the object exposed.20. A transmittance measurement apparatus comprising: a first beamsplitting part for generating first split beam having a specificpolarization from light emitted from a light source; a second beamsplitting part for generating, from said light emitted from the lightsource, a second split beam having said specific polarization; a firstdetector for detecting a light intensity of the first split beam; and asecond detector for detecting a light intensity of the second splitbeam, wherein a transmittance of a sample is measured based on adifference between detection results by said first and second detectorswith and without the sample in the first or second split beam.
 21. Atransmittance measurement apparatus according to claim 20, wherein saidtransmittance measurement apparatus may further comprise a stage forcarrying the sample, removing and inserting the sample onto and out ofan optical axis of either of the first or second split beam.
 22. Atransmittance measurement apparatus according to claim 20, wherein thelight source is an ultraviolet pulse laser.
 23. A transmittancemeasurement apparatus comprising: a first optical member for reflectingand transmitting light from a light source to generate reflected andtransmitted beams; a second optical member for transmitting thereflected beam to generate a first split beam having a specificpolarization; a third optical member for reflecting the transmitted beamto generate a second split beam having said specific polarization; afirst detector that detects a light intensity of the first split beam;and a second detector that detects a light intensity of the second splitbeam, wherein a transmittance of a sample is measured based on adifference between detection results by the first and second detectorswith and without the sample in the second split beam.
 24. Atransmittance measurement apparatus according to claim 23, wherein thefirst and second split beams have an equal number of reflection times onsaid optical members and equal polarization characteristics at thereflections, as well as an equal number of transmission times on saidoptical members and equal polarization characteristics at thetransmissions.
 25. A transmittance measurement apparatus comprising: afirst optical member for reflecting and transmitting light emitted froma light source to generate reflected and transmitted beams, and uses thereflected beam as a first split beam having a specific polarization; asecond optical member for transmitting and reflecting the transmittedbeam to generate transmitted and reflected beams; a third optical memberfor reflecting the transmitted beam generated by said second opticalmember to generate a second split beam having said specificpolarization; a first detector for detecting a light intensity of thefirst split beam; and a second detector for detecting a light intensityof said second split beam, wherein a transmittance of a sample ismeasured based on a difference between detection results by said firstand second detectors with and without the sample in the second splitbeam.
 26. A transmittance measurement apparatus according to claim 25,wherein the first and second split beams have an equal number ofreflection times on said optical members and equal polarizationcharacteristics at the reflections, while said second optical membertransmits a linear polarization component orthogonal to that havingtransmitted said first optical member.
 27. A transmittance measurementapparatus comprising: a first optical member for reflecting andtransmitting light emitted from a light source to generate reflected andtransmitted beams, and uses the reflected beam as a first split beamhaving a specific polarization; a second optical member for transmittingand reflecting the transmitted beam to generate transmitted andreflected beams; a third optical member for transmitting the reflectedbeam generated by said second optical member to generate a second splitbeam having said specific polarization; a first detector for detecting alight intensity of said first split beam; and a second detector fordetecting a light intensity of said second split beam, wherein atransmittance of a sample is measured based on a difference betweendetection results by said first and second detectors with and withoutthe sample in the second split beam.
 28. A transmittance measurementapparatus according to claim 27, wherein the first and second splitbeams have an equal number of reflection times on said optical membersand equal polarization characteristics at said reflections, while saidthird optical member transmits a linear polarization componentorthogonal to that having transmitted the first optical member.
 29. Atransmittance measurement apparatus comprising: a first optical memberfor reflecting and transmitting light emitted from a light source togenerate reflected and transmitted beams, and uses the transmitted beamas a first split beam having a specific polarization; a second opticalmember for transmitting and reflecting the transmitted beam to generatetransmitted and reflected beams; a third optical member for reflectingthe transmitted beam generated by said second optical member to generatea second split beam having said specific polarization; a first detectorfor detecting a light intensity of the first split beam; and a seconddetector for detecting a light intensity of the second split beam,wherein a transmittance of a sample is measured based on a differencebetween detection results by said first and second detectors with andwithout the sample in the second split beam.
 30. A beam splittingapparatus according to claim 29, wherein the first and second splitbeams have an equal number of transmission times on said optical membersand equal polarization characteristics at the transmissions, while saidthird optical member reflects a linear polarization component orthogonalto that having reflected on said first optical member.
 31. Atransmittance measurement apparatus comprising: a first optical memberfor reflecting and transmitting light emitted from a light source togenerate reflected and transmitted beams, and uses the transmitted beamas a first split beam having a specific polarization; a second opticalmember for transmitting and reflecting the reflected beam to generatetransmitted and reflected beams; a third optical member for transmittingthe reflected beam generated by said second optical member to generate asecond split beam having said specific polarization; a first detectorfor detecting a light intensity of said first split beam; and a seconddetector for detecting a light intensity of said second split beam,wherein a transmittance of a sample is measured based on a differencebetween detection results by said first and second detectors with andwithout the sample in the second split beam.
 32. A transmittancemeasurement apparatus according to claim 31, wherein the first andsecond split beams have an equal number of transmission times on saidfirst and second optical members and equal polarization characteristicsat the transmissions, while said third optical member reflects a linearpolarization component orthogonal to that having reflected on said firstoptical member.
 33. A transmittance measurement apparatus according toone of claims 23, 25, 27, 29 and 31, wherein the first, second, andthird members are optical elements having the same reflectance andtransmittance properties.
 34. A transmittance measurement apparatusaccording to one of claims 23, 25, 27, 29 and 31, wherein the first,second, and third members are plane parallel plates.
 35. A transmittancemeasurement apparatus according to claim 34, wherein the plane parallelplates are arranged such that an incident angle is 45°.